R. Townley Roofing

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What Life span to expect from your roof

What Life span to Expect from you Roof

Cedar Shakes


One of the most difficult types of roofs to estimate the lifespan for is the cedar shake or shingle roof.  In considering your client’s options, whether buyer or seller, keep in mind the following:


Average Lifespan

The average lifespan of a No. 1 medium split cedar shake is about 17—18 years.  Of the thousand of roofs we have replaced, most are 17—18 years or older.


Type of Shake/Shingle

In the West, it has been our experience that split cedar shakes tend to last longer than either Cedar Shingles or Tapersawn shakes—both of which are sawn on 2 sides.



Cedar Shake Roofs come in 2 thicknesses: Mediums (1/2” - 5/8” thick at butt) and Heavies (3/4” - 1  1/2”).  The vast majority (over 90%) of shake roofs are mediums.



The quality of a shake is determined by several characteristics including the absence of knots, number of growth rings per inch which measures density and age, and the direction of grain.  The minimum standard for roofing is defined as a Number 1 Grade Shake which must meet the strict ICBO requirements.  These Shakes must be free of knots, have a minimum number of growth rings per inch, and a maximum of 20% flat grain.  Over the years, this has been the most common shake used for reroofing.

In recent years, mills have offered a higher quality shake called a Premium Shake.  These shakes are manufactured under strict guidelines and must be 100% “Vertical Grain” (also known as “Edge Grain”).

Finally, in the last decade, as the cost of cedar has risen, the relative expense of having a pressure treated shake has become more affordable.  The treatment process results in a 30 year warranty and is known as a CCA treatment.  (Similar to the Osmose and Wolmanized process for lumber.)



The standard Exposure (the amount of shake you see on each course of roofing_ for a cedar shake roof installed with 24” shake is 10 inches.  When the exposure is reduced to 7 1/2-8” per course, the roof now becomes a 3 ply roof (at any given spot there are three layers of cedar as opposed to two with a 10 inch exposure).  A 3 ply roof will usually last several years longer than a 2 ply roof.


Steeper roofs last longer than low-pitched roofs because leaves, pine needles, moss and fungus are less inclined to retain moisture and cause deterioration of the shakes.



Although beautiful, cedar shake roofs do require periodic maintenance to help them last longer.  Keeping debris such as pine needles, leaves and moss of the roof is essential.  Cleaning with water or air is also suggested on roofs younger than 10 year.



Although shakes tend to “breath” through the spaced sheeting, lack of adequate ventilation can create problems and may reduce the roof’s lifespan.  This is especially true if the shakes have been installed over a solid deck or if a dryer or bathroom has been vented into the attic.



While the quality of materials is significant in determining the duration of a roof’s life, the installation methods are equally important.  While most roofs are installed according to generally acceptable practice occasionally we will find a house built by a general contractor  who hired sub-par roofers to save money.  Those roofs sometimes exhibit excessive “shiners” (fasteners visible between shakes) and shakes which have been “butt stapled” to nail down warped board in an effort to make the house more presentable for sale.  Both of these problems  can dramatically reduce the life of a roof.



In determining what repairs would be needed to get a shake roof to certify for 2 year, a roofer must consider the following:

1. The condition of the wood—worn areas between shakes missing shakes or ridge, exposed felt, rotted butts, excessive splitting, curled shakes.

2. The number of shakes which need to be replaced.  This is determined by walking the roof and actually counting the number of shakes and / or ridge which need to be repaired.  The contractor should be conservative and include an additional percentage which will be needed as some shakes will be damaged during the repair process.

3.  Determine the efficacy of washing and treating the roof.  While a treatment is always a good way to extend roof life, pressure washing can sometimes create more problems and damage the existing roof.